#include <fstream>
#include <vector>
#include <stack>

using namespace std;

ifstream fin("ciclueuler.in");
ofstream fout("ciclueuler.out");

vector<int> v[100001];
vector<int>::iterator it;

int n,m,i,aux,nod,x,y;
stack<int> s;

void sterge_muchia(int x, int y)
{
    for (vector<int>::iterator it = v[x].begin(); it != v[x].end(); it ++)
        if (*it == y)
        {
            v[x].erase(it);
            return;
        }
    return;
}

int main()
{
    fin>>n>>m;
    for (i=1;i<=m;i++)
    {
        fin>>x>>y;
        v[x].push_back(y);
        v[y].push_back(x);
    }
    for (i=1;i<=n;i++)
        if (v[i].size() % 2 != 0 || v[i].empty())
        {
            fout<<-1;
            return 0;
        }
    nod = 1;
    s.push(nod);
    while (!s.empty())
    {
        nod = s.top();
        if (!v[nod].empty())
        {
            aux = v[nod].back();
            v[nod].pop_back();
            sterge_muchia(aux, nod);
            s.push(aux);
        }
        else
        {
            aux = s.top();
            s.pop();
            if (!s.empty())
                fout<<aux<<" ";
        }
    }
    return 0;
}